Experimental models of inflammatory bowel disease are being defined in inbred strains of rats. Lymphocytes reacting to an antigen found in the colon or to an exogenous antigen which localizes in the colon may produce inflammatory changes. We are attempting to determine the specific lymphocyte population which produces those responses and evaluate means of controlling their functional activity. A possible means of controlling disease activity in our experimental animals will then be explored with the possibility of clinical application to patients with inflammatory bowel disease.